Polyodon spathula
Polyodon spathula (''American paddlefish)' Kingdom: '''Animalia Phylum: Chordata Class: Actinopterygii Order: Acipenseriformes Family: Polyodontidae Genus: Polyodon Species: Polyodon spathula Environment: milieu, climate zone, depth range, distribution range: Freshwater; demersal; potamodromous; depth range 2 - ? m. Subtropical; 10°C - 18°C; 49°N - 29°N, 112°W - 77°W. Distribution: North America: Mississippi River basin from southwestern New York to Montana and south to Louisiana; Gulf Slope drainagaes from Mobile Bay in Alabama, to Galveston Bay in Texas, USA. Formerly in Great Lakes basin, probably extirpated. At least one country reports adverse ecological impact after introduction. Size, weight, age: Max. length: 2.21 m, common length: 1.20 m; weight: 90.7 kg; age: 55 years Short description: American paddlefish are among the largest and longest-lived freshwater fishes in North America. They have a shark-like body, average 1.5 m (4.9 ft) in length, weigh 27 kg (60 lb), and can live in excess of thirty years. For most populations the median age is five to eight years and the maximum age is fourteen to eighteen years. The age of American paddlefish is best determined by dentary studies, a process which usually occurs on fish harvested during snagging season, a popular sport fishing activity in certain parts of the U.S. The dentary is removed from the lower jawbone, cleaned of any remaining soft tissue, and cross-sectioned to expose the annual rings. The dentary rings are counted in much the same way a tree is aged. Dentary studies suggest that some individuals can live 60 years or longer, and that females typically live longer and grow larger than males. American paddlefish are smooth-skinned and almost entirely cartilaginous. Their eyes are small and directed laterally. They have a large, tapering operculum flap, a large mouth, and a flat, paddle-shaped rostrum that measures approximately one-third of their body length. During the initial stages of development from embryo to hatchling, American paddlefish have no rostrum. It begins to form shortly after hatching. The rostrum is an extension of the cranium, not of the upper and lower jaws or olfactory system as with the long snouts of other fishes. Other distinguishing characteristics include a deeply forked heterocercal caudal fin and dull coloration, often with mottling, ranging from bluish gray to black dorsally grading to a whitish underbelly. Biology: Usually inhabits water deeper than 1.2 m in slow-flowing large rivers, lakes, and impoundments. Feeds on plankton. The extended upper jaw (= paddle) may help to channel plankton into the mouth. Threatened due to over harvesting, habitat loss and pollutio. Life cycle and mating behavior: American paddlefish are long-lived, sexually late maturing pelagic fish. Females do not begin spawning until they are seven to ten years old, some as late as sixteen to eighteen years old. Females do not spawn every year, rather they spawn every second or third year. Males spawn more frequently, usually every year or every other year beginning around age seven, some as late as nine or ten years of age. American paddlefish begin their upstream spawning migration sometime during early spring; some begin in late fall. They spawn on silt-free gravel bars that would otherwise be exposed to air or covered by very shallow water were it not for the rises in the river from snow melt and annual spring rains that cause flooding. Although availability of preferred spawning habitat is essential, there are three precise environmental events that must occur before American paddlefish will spawn. The water temperature must be from 55 to 60 °F (13 to 16 °C); the lengthened photoperiod which occurs in spring triggers biological and behavioral processes that are dependent on increasing day length; and there must be a proper rise and flow in the river before a successful spawn can occur. Historically, American paddlefish did not spawn every year because the precise environmental events only occurred once every 4 or 5 years. American paddlefish are broadcast spawners, also referred to as mass spawners or synchronous spawners. Gravid females release their eggs into the water over bare rocks or gravel at the same time males release their sperm. Fertilization occurs externally. The eggs become sticky after they are released into the water and will attach to the bottom substrate. Incubation varies depending on water temperature, but in 60 °F (16 °C) water the eggs will hatch into larval fish in about seven days. After hatching, the larval fish drift downstream into areas of low flow velocity where they forage on zooplankton. Young American paddlefish are poor swimmers which makes them susceptible to predation. Therefore, rapid first-year growth is important to their survival. Fry can grow about 1 in (2.5 cm) per week, and by late July the fingerlings are around 5–6 in (13–15 cm) long. Their rate of growth is variable and highly dependent on food abundance. Higher growth rates occur in areas where food is not limited. The feeding behavior of fingerlings is quite different from that of older juveniles and adults. They capture individual plankton one by one, which requires detection and location of individual Daphnia on approach, followed by an intercept maneuver to capture the selected prey. By late September fingerlings have developed into juveniles, and are around 10–12 in (25–30 cm) long. After the 1st year their growth rate slows and is highly variable. Studies indicate that by age 5 their growth rate averages around 2 in (5.1 cm) per year depending on the abundance of food and other environmental influences. Main reference: Page, L.M. and B.M. Burr, 2011. A field guide to freshwater fishes of North America north of Mexico. Boston : Houghton Mifflin Harcourt, 663p. IUCN Red List Status: VULNERABLE (''VU)' '''CITES: Appendix II: International trade monitored CMS: Not Evaluated Threat to humans: ?''' ''Human uses:' Fisheries: commercial; aquarium: public aquariums. Category:Polyodontidae, Paddlefishes